1. You're almost already approved when you get there
Once you get into the interview room, you’ve already been pre-screened to ensure you’re not on any international watch lists, terror-threat lists, or just general, the-US government-doesn’t-like-you lists. Sometimes they even have your pre-printed approval paper face down on the desk when you walk in. (Just don't be all like, "Hey, is that my approval in front of you? Come on, you can tell me.") So once you get the call, the hard part is over. It’s not a job interview, just go in and relax.
2. They're not going to ask you much
Aside from basic biographical information (name, birthdate, address, etc.), questions should be limited to the following: